Transceive and tracking antenna horn array



Dec. 2, 1969 J. D- Bowris, JR

Filed May 19, 1967 Rm m F MW 5 D M d WWW ATTORNEY United States Patent M3,482,251 TRANSCEIVE AND TRACKING ANTENNA HORN ARRAY John D. Bowes, Jr.,Mountain View, Calif., assignor to Philco-Ford Corporation,Philadelphia, Pa., 21 corporation of Delaware Filed May 19, 1967, Ser.No. 639,747 Int. Cl. H01q 13/02 US. Cl. 343-776 Claims ABSTRACT OF THEDISCLOSURE Transceive and tracking antenna horn array utilizing circularcenter horn surrounded by four adjacent square outer tracking horns,each outer horn having a sector removed to accommodate center horn andeach outer horn containing a diagonal dielectric plate to compensate forremoved sector.

This invention relates to antennas and more particularly to an array ofantenna horns for performing transmit/ receive (transceive) and trackingfunctions.

In order to communicate with a satellite from a ground station, atransceive antenna system is required for prime communications, and atracking antenna system is required in order to obtain direction-relatedsignals to enable any misorientation of the antenna with the satelliteto be corrected. Heretofore, transceive and tracking antenna systemshave used a rectangular center horn for transmitting and receiving themain communication signal to and from the satellite and four outertracking horns spaced around the center horn for providing fourdifferent versions of the signal for tracking purposes. Appropriateantenna reflectors were provided to focus the received signal into aconcentrated beam directed at the center horn, with a portion of theless-concentrated part of the received signal surrounding theconcentrated beam being collected by the outer horns. Representativehorn arrays of the above type are shown in US. Patents 2,929,- 056 toPage (Mar. 15, 1960) and 3,045,238 to Cheston (July 17, 1962).

Prior art horn arrays of the above type had various difiicultiesassociated therewith, namely: (1) the radiated signal pattern had largesidelobes, resulting in transmitted signal loss and low receivedsignal-to-noise ratio, (2) empty spaces around the center horn caused apartial loss of the less-concentrated part of the received signal,thereby decreasing tracking efliciency, and (3) the centers of phases ofthe outer horns were relatively widely spaced from each other, whichalso resulted in ineflicient tracking.

Arrangements have also been proposed, as typified in Patent 2,677,055 toAllen (Mar. 27, 1954), in which the transceive and tracking antenna hornarray consists of four adjacent rectangular outer horns surrounding acircular center horn. However these arrangements, while eliminating someof the difiiculties of the aforementioned arrays, suffered from theinability to couple and receive a large amount of signal energyefiiciently through the center horn. In addition, they were unable totrack accurately because the outer horns were unable to receive acircularly polarized signal due to the presence of the removed sectorwhich accommodated the center horn.

The horn array of the present invention overcomes the disadvantages ofthe aforenoted prior art arrangements. Accordingly several objects ofthe present invention are: (1) to provide an antenna horn array whichhas an improved radiation pattern with smaller sidelobes than prior artarrangements, (2) to provide a horn array in which a maximum of theless-concentrated part received signal surrounding the focused beamthereof is collected and 3,482,251 Patented Dec. 2, 1969 utilized by theouter tracking horns, (3) to provide such an arrangement in which thecenters of phases of the tracking horns are closely spaced, therebyresulting in improved tracking, (4) to provide such an arrangement inwhich large amounts of power can be transceived efliciently by a centerhorn, and (5) to provide such an arrangement in which the outer trackinghorns can receive a circularly polarized signal. Other objects andadvantages of the present invention will become apparent from aconsideration of the following description thereof.

SUMMARY According to the present invention a transceive and trackingantenna horn array utilizes a conical center horn surrounded by fouradjacent square outer horns, each of which has a sector removed so thatthe four outer horns can closely surround the center horn. Each of thefour outer horns has a dielectric plate fitted diagonally betweenopposing corners thereof in order to provide electrical compensation forthe removed sector thereof.

DRAWINGS FIG. 1 shows a perspective front view of the antenna horn arrayof the invention, FIG. 2 shows a perspective rear view thereof, and FIG,3 shows a front view thereof.

DESCRIPTION As shown in the three views thereof, the transceive andtracking antenna horn array of their invention comprises a circularconical center horn 10 having a relatively small apex portion 10a and arelatively large flared portion 10b. Surrounding the center horn arefour outer tracking horns 16, 18, 20 and 22, each of which has arelatively small square apex portion, such as portion 20a of horn 20,and a relatively large flared portion, such as portion 20b of horn 20.The flared portions are not completely square but have an arcuate sectorin lieu of one corner thereof in order to accomodate the flared portion10b of the circular center horn. The four tracking horns and the centerhorn may be formed individually and then may be assembled so that thefour tracking horns adjoin or lie closely to each other and the centerhorn at their forward or flared ends. The outer walls of the trackinghorns will thus define an outer square and their arcuate segments willdefine an inner circle which accommodates the center horn. Alternativelythe tracking horns can be partially formed without arcuate segments andthen attached to the center horn so that the flared end thereof willalso serve as the arcuate segments of the tracking horns. The outer orfull walls of the tracking horns are perpendicular to the front planeformed by the flared ends of all five horns. The inner or partial wallsof the tracking horns, such as wall 24, are not perpendicular to saidfront plane but are angled as shown to produce the taper of the trackinghorns. At the front of the array the inner walls of adjacent hornsdesirably abut one another as shown so as to define four segments, suchas segment 25, which perpendicularly connect the outer square defined bythe outside walls of the outer horns with the outside surface of thecenter horn. Coupled to the rear or apex end of each of the outer hornsare four circular-to-linear polarization converters 26, 28, 30 and 32which may be of conventional form. Tracking circuitry (not shown) iscoupled to the outputs of the polarization converters.

According to the invention, four dielectric compensating plates 34, 36,38 and 40 are fitted within the outer horns. As shown in the cutawayVieWs of horn 18 in FIGS. 1 and 2, each of the dielectric compensatingplates extends between the diagonally opposite corners of its respectiveouter horn and runs along it respective horn from the flared portion tothe point where the arcuate segment vanishes from a cross section toform a square horn cross section. To provide good matching between thehorns and the polarization converters, each of the dielectriccompensating plates has a pointed section, such as section 36a of plate36, which extends through the end of the arcuate portion into the squareportions of these horns. Each of the dielectric compensating platesshould have a dielectric constant of from 2 to 3. Dielectric materialssuitable for this purpose are those sold under the trade names Rexoliteand Plexiglas.

The dimensions of the center and outer horns are governed in the usualfashion in inverse proportion to the frequencies of the transmitted andreceived signals. In one operational embodiment of the invention thesignal transmitted through the center horn ranged from 7.9 to 8.4- gHz.and the signal received by the center horn and the four outer hornsranged from 7.25 to 7.75 gHz. In this embodiment the dimensions of eachside of the flared portion of each outer horn was about 3 inches. Thusthe outer square had a dimension of about six inches on a side. Inanother embodiment of the invention wherein the transmitted and receivedsignals were on the order of 3-4 gHz., the dimension of a side of theflared portion of each outer horn was about 12 inches.

Since the transmitted and received signals are both supplied andreceived at the apex portion a of the center horn, it is necessary toseparate these signals and couple them to separate transmit and receivewaveguides (not shown) so that they can be processed by a transmitterand a receiver (not shown). One suitable arrangement for this purposeutilizes an orthogonal mode transducer coupled to the end of the apexportion 10a. One output of the orthogonal transducer is coupled to oneterminal of a 90 hybrid section via a 90 twist waveguide section and theother output of the orthogonal mode transducer is coupled to anotherterminal of the 90 hybrid section via a phase adjusting waveguidesection. One end of a transmit waveguide is coupled to a third terminalof the 90 hybrid section via a received signal frequency rejectingfilter, and one end of a receive waveguide is coupled to the fourthterminal of the 90 hybrid section via a transmit signal frequencyrejecting filter. The other ends of the transmit and receive waveguidesare coupled to a transmitter and a receiver, respectively.

The signals received by the tracking horns, after translation throughthe polarization converters 26, 28, 30 and 32, are coupled to errorsignal circuitry (not shown) which generates horizontal and verticalerror signals for driving positioning controls which correct theorientation of the antenna with respect to the satellite. In oneembodiment a vertical error signal was synthesized by subtracting thesum of the output signals from horns 16 and 18 from the sum of thesignals from horns 20 and 22. A horizontal error signal was synthesizedby subtracting the sum of the signals from horns 16 and 22 from the sumof the signals from horns 18 and 20.

The most advantageous antenna reflector arrangement for the horn arrayis a Cassegranian system (such as shown in FIG. 25-10 on p. 25-12 of theAntenna Engineering Handbook, by Jasik, McGraw-Hill, 1961) in which thesignals travel from the horn array to the satellite (and vice versa) viaa hyperboloid subrefiector and a circular paraboloid main reflector. Theorientation of the entire assembly, including the horn array,subreflector, and main reflector, will be aimed at the satellite bymeans of a servomechanism arrangement which is driven by theaforementioned vertical and horizontal error signals.

OPERATION In operation, the transmitted and received signals aresupplied through the center horn ring in a circular polarization mode inconvention fashion. Since the center horn is circular, it will producesmaller sidelobes than a rectangular center horn and accordingly lessscattering will result, providing more eflicient transmission andreception.

As stated, the received signal will be focused into the flared end 10bof the center horn. A less-concentrated part of the received signalsurrounding the focused beam will be collected by the four outertracking horns. The amount of signal collected by each tracking hornwill be equal when the array is aimed correctly and unequal when thearray is not aimed correctly. When the array is aimed incorrectly anappropriate error signal will be produced which will cause theorientation of the array to be corrected, as aforenoted.

Since the four outer horns completely surround the center horn withoutleaving any vacant space around the outside of the center horn, amaximum amount of the less-concentrated part of the signal surroundingthe focused beam will be captured by the outer horns, thereby supplyinga maximum amount of signal to the tracking circuitry, so that hightracking efficiency results. Tracking will also be aided because thetight packing of the outer horns around the center horn will cause thecenters of the phases of the outer horns to be closely spaced.

According to the invention, the arcuate sector of each outer horn whichaccommodates the center horn is com pensated for electrically by thepresence of a respective one of the dielectric compensating plates 34,36, 38 and 40'. Each dielectric plate delays the component of theelectric field in its tracing horn which is parallel to the dielectricplate. This component of the electric field has a higher than normalphase velocity as a result of the removed sector and the dielectricplate provides a compensating delay. The dielectric plates thereby allowthe outer tracking horns to operate with any sense of linear or circularpolarization. Thus the tracking function can be effected accurately.

While there has been described what is at present considered to be thepreferred embodiment of the invention it will be apparent that variousmodifications and other embodiments thereof will occur to those skilledin the art within the scope of the invention. Accordingly, it is desiredthat the scope of the invention be limited by the appended claims only.

I claim:

1. A transceive and tracking antenna horn array, comprising:

(a) a conical center horn having a circular rear end of relatively smalldiameter and a circular front end of relatively large diameter,

(b) four outer horns positioned around said center horn, each outer hornhaving a small rear end and a relatively large front end, the front endof each horn having a partially rectangular cross Section defined byfirst and second mutually perpendicular outer walls which meet at afirst corner, a first inner wall perpendicular to and abutting saidfirst outer wall to form a second comer, a second inner walllperpendicular to and abutting said second outer wall to form a thirdcorner, and a tapered arcuate inner wall joining said first and secondinner walls, said tapered arcuate inner walls of said four outer hornstogether defining an opening generally conforming to the front end ofsaid center horn, and

(c) four dielectric compensating plates, each positioned in one of saidouter horns and extending from the second to the third corners thereof.

2. The array of claim 1 wherein a circular-to-linear polarizationconverter is coupled to the rear end of each of said outer horns.

3. The array of claim 1 in which said inner walls of said outer hornsabut the outside surface of said center horn and abut each other in fourpairs so that the front ends of said outer walls of said outer hornsform a rectangle with the abutting ends of said inner walls forming foursegments, each perpendicularly connecting said outer rectangle to saidinner horn.

4. The array of claim 1 wherein the front surface formed by the frontends of said center horn and said four outer horns is planar, each ofsaid outer horns has a square cross section, except for said arcuateinner wall thereof, and the two outer walls of each of said outer hornsare perpendicular to the front surface of said array and are planar fromsaid front to said rear ends thereof.

5. The array of claim 1 wherein each of said compensating plates has adielectric constant from 2 to 3 and extends from the front to the end ofits arcuate segment of its respective horn along said second and thirdcorners thereof.

6. A transceive and tracking antenna horn assembly, comprising:

(a) four outer rectangular horns, each having a relatively small apexportion and a relatively large flared portion, each of said flaredportions having an arcuate sector in lieu of one corner thereof, saidfour horns being positioned so that the four arcuate sec tors generallydefine a circular opening surrounded by said four horns with the outsidesurfaces of said four horns generally defining a rectangle.

(b) a circular center horn having a relatively small apex portion and arelatively large flared portion, said flared portion being positioned insaid circular opening, and

(c) four dielectric compensating plates, each extending across arespective one of said outer horns between the diagonally-oppositecorners thereof.

7. The array of claim 6 wherein said center horn and said outer hornsare joined together in a unitary structure with the arcuate sectors ofsaid outer horns and the flared portion of said center horn beingunitary.

8. The array of claim 6 wherein a circular-to-linear polarizationconverter is coupled to the apex ends of each of said four outer horns.

9. The array of claim 6 wherein the apex ends of said four outer hornsare square and the flared ends thereof are square, except for saidarcuate sectors, whereby the outside surfaces of said outer hornsgenerally define a square.

10. The array of claim 6 wherein each of said compensating plates has adielectric constant from 2 to 3 and extends along its respective hornfrom the start of the arcuate portion to the flared portion thereof.

References Cited UNITED STATES PATENTS 2,425,488 8/1947 Peterson et al343-776 ELI LIEBERMAN, Primary Examiner U.S. Cl. X.R. 343-785, 786

